Mandate can be granted expressly or tacitly.
Civil Code
2015 English source edition · Current applicability not established.
This is the 2015 English-language edition attributed in its front matter to the Ministry of Justice. Eri Atlas has not independently verified the translation, later changes, or whether the text is currently in force. Nine passages are incomplete in the available scan and are identified where they occur.
Article 2375
Granting of Mandate · Preserved transcription; page attribution imported from the source collection. Verify against the original.
Where the juridical act to be performed by the mandatary is under the law to be made in a prescribed form, such form shall be complied with in granting mandate.
When a juridical act has been performed in the name of another person, the other party who, on the basis of a declaration or conduct of that other person, has presumed and in the given circumstances could reasonably presume the existence of a sufficient mandate, may not have invoked against him the inaccuracy of this presumption.
If a mandate, which has been made public pursuant to law or usage, contains restrictions which are so unusual that the other party should not have anticipated their existence, they cannot be invoked against such party, unless he had actual knowledge of them.